1. Field of the Invention
This invention relates to a method of filling a cable anchorage with a filling material and to cable anchorages formed by such a method.
The invention is especially applicable to the cable stays in a cable stayed structure where there is a particular need for an anchorage which can withstand cyclical loading, but is in principle applicable to other anchorages of other cables, e.g. prestressing cables. The cable may consist of a single cable element or a plurality of cable elements, each element being for example a wire or a strand (a strand is a multi-wire element). For simplicity we shall generally use the term "wire" in this description.
In the construction of certain types of structures such as roofs or bridges it is common to use cable stays which transmit forces from for example a slab or deck to a column. In the past such stays were manufactured using conventional cables which were anchored at both ends in dead heads each having a conical internal shape in which the wires or the strands spread apart and which were filled with a mixture of tin and other fusible metals at low temperatures. Modern advances in this technique have introduced the use of tendons made up of parallel wires or strands which are anchored in heads filled with a special mortar of which the binding element is an epoxy resin. At the same time the ends of the wires or strands are anchored adjacent the head in an anchor plate by wedges, button heads or by some other type of anchorage.
It is a considerable problem however to obtain a filling material (especially for large tendons where the volume of material required is large) which does not shrink and whose curing temperature is within limits which do not affect the steel of the wires. Such considerations have led to the use of mixtures of epoxy resin, mineral powder and aggregates, in which the quantity of mineral powder and aggregate is great enough to reduce shrinkage of the epoxy resin to a minimum and to prevent any undue rise in temperature during the curing of the epoxy resin. The powder may be of silex or zinc or some other metal and the aggregate may be any type of heavy stone or steel balls.
However such a filling material is very thick and viscous and presents a number of problems in use. In order to inject the filling material into the anchorage a powerful injection pump is required. Even when such an injection pump is used, the use of such a thick filling material renders it difficult for the filling material to penetrate all the small spaces between the wires in the anchorage, especially when the filling operation is conducted on site. It is possible to achieve a better filling of the anchorage in factory conditions, but this would necessitate transporting the tendon to the site in its completely assembled form.